# NiCl_3 is a strong electrolyte. How do you determine the concentration of each of the individual ions in a 0.400 M NiCl_3 solution?

I think you mean $N i C {l}_{2}$.
In aqueous solution, nickel chloride gives a beautiful green solution, which we would represent as ${\left[N i {\left(O {H}_{2}\right)}_{6}\right]}^{2 +}$ or simply as $N {i}^{2 +} \left(a q\right)$. Two (aquated) chloride counterions, $C {l}^{-} \left(a q\right)$, are along for the ride.
The concentration of the hexaqua complex is (clearly) $0.400 \cdot m o l \cdot {L}^{-} 1$. The concentration of the chloride counterions is $0.800 \cdot m o l \cdot {L}^{-} 1$.